1. Field of the Invention
This invention relates to a valve for regulating the pressure of vapor or liquid which incorporates the ability or relieving pressure if it exceeds the regulated level by a predetermined amount.
2. Description of the Prior Art
In various fluid supply systems, it is often necessary to regulate the pressure level of a fluid and, at the same, to relieve pressure if the pressure of the fluid on the regulated side or the unregulated side of the valve exceeds a predetermined amount.
For example, in cryogenic supply systems for oxygen, nitrogen, and the like, gas is supplied to a pressure building regulator value from a pressure building coil connected to the bottom of the cryogenic liquid tank, which supplies the gas at a regulated pressure to the top of the tank. The gas in the tank, at the pressure level regulated by the pressure building regulator valve, forces the liquid out of the tank of the desired pressure through a liquid supply line. Because the tank pressure may increase above the regulated level due to evaporation of the cryogenic liquid in the tank, a second regulating valve must be used. This second regulating valve is sometimes known as an "economizer" regulator, since it permits the gas to flow from the tank to the gas supply line or to a vent line. In addition, it is possible that the level of the gas pressure in the pressure building coil may be too high to permit the gas to be supplied to the tank. In this case, a third valve must be used to relieve excess pressure in the pressure building coil.
Thus, it can be seen that three valves may be needed. A first valve to regulate pressure from the pressure building coil to the tank top. A second valve to relieve excess pressure in the tank top. And, a third valve to relieve excess pressure in the pressure building coil.